Molecular Dynamics Compared to Hydrodynamics for Rayleigh-Taylor Instability

A massively parallel molecular-dynamics (MD) simulation of some 100 million particles is compared to theoretical Navier-Stokes (NS) predictions, continuum NS simulations, and experimental observations of the Rayleigh-Taylor fluid instability. Smaller MD simulations were performed to verify the initial exponential rise of a single bubble, as predicted analytically for both miscible and immiscible fluids. The penetration of spikes of heavy fluid into light, along with bubbles of light rising into heavy, grows as the square of time at long times--with experiment and both atomistic and continuum computer simulation in 20% agreement. However, part of the differences may be due to dependence upon initial conditions, whose influence on the growth of individual modes was studied for two different cases: an initial interface formed by a single sinusoidal perturbation vs. one perturbed only by thermal fluctuations